No abstract

No abstract

We report a simple method for preparing copper(II) molybdate (CuMoO 4) powders via a combustion-like process. A gel was first prepared by the polymerizable complex method, where citric acid was used as a complexing and polymerizing agent and nitric acid was used as an oxidizing agent. The thermal decomposition behavior of the (CuMo)-precursor gel was studied by thermogravimetry-differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). We observed that the crystallization of CuMoO 4 powder was completed at 450°C. The obtained homogeneous powder was composed of grains with sizes in the range from 150 to 500 nm and exhibited a specific surface area of approximately 5 m 2 /g. The average grain size increased with increasing annealing temperature. The as-prepared CuMoO 4 crystals showed a strong green photoluminescence emission at room temperature under excitation at 290 nm, which we mainly interpreted on the basis of the JahnTeller effect on [MoO 4 2− ] complex anions. We also observed that the photoluminescence intensity increased with increasing crystallite size.

Submicronic CoAl 2 O 4 powders were prepared by double decomposition reaction between solid LiAlO 2 and molten KCoCl 3 at 500 • C for 24 h. The reaction mechanism involves the dissolution of LiAlO 2 shifted by the precipitation of CoAl 2 O 4 until complete transformation and the reaction leads to powders with a very homogeneous chemical composition. The powders obtained were mainly characterized by XRD, FTIR, ICP, X.EDS, electron microscopy and diffraction and diffuse reflexion. The blue pigments obtained exhibit a high thermic stability allowing their use for the colouring of ceramic tiles.

The aim of this study was to detennine the effect of different complexing agents and of the annealing tem perature on the structural, morphological and optical properties of the synthesized precursors. Thus, cobalt aluminate nanoparticles were prepared by the sol-gel method using polyacrylic acid, glycine or citric acid as complexing agents. The synthesis performed at 500 °C for 5 hours led to dark green powders composed of solid solutions denoted Co 2+ [ Agci-x) Co�;i]O4 and of amorphous alumina (39.8wt%). Calcination at temperatures above 900 °C caused the powder colour to change from dark green to blue. A direct spinel structure Co 2+ [ Al� + ] 04 is all the more achieved as the annealing temperature is high. The powder obtained using polyacrylic acid as the complexing agent at 900 °C for 5 hours revealed the best morphology; it consisted of agglomerates of primary particles with a quasi-spherical shape and a size in the range 20-40 nm.

No abstract

Nanocrystals of zinc-cobalt molybdate (Zn1-xCc>xMo04) were prepared by the glycine-nitrate process (GNP) route with a glycine/nitrate ratio of 2:3 and compared to the solid state synthesis. The obtained powders were characterized by thermal analysis (TGA-TDA), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The morphology was examined by scanning electron microscopy (SEM) and Brunauer-Ernrnett-Teller (BED. The particle size was determined by transmission electron micros copies (TEM). UV-Visible spectroscopy and CIE L*a*b* colorimetric parameters have been used for the colour characterisation and measurement. The compounds obtained present two single-phased domains regardless of the synthesis method. The first domain of blue colour corresponding to a level of cobalt x such as: 0 = x S 0.3, isostructural with a-ZnMo04 of triclinic symmetry and the second domain of green colour, for cobalt x levels such as: 0.45 = x S 1 isostructural with cr-CoMo04 of monoclinic structure. The Zno,7Coo.3Mo04 powders obtained at 700 °c by GNP route and synthesized in acidic environment were fonned of particles of quasi-spherical morphology, with average size of crystallites estimated between 80-140 nm.

A sol-gel method was proposed to prepare copper II molybdate α-CuMoO 4 powders. A gel was first obtained via the polymerizable complex method, using citric acid as complexing and polymerizing agent, dried at 120 1C and decomposed at 300 1C. A calcination in the temperature range 400-500 1C for 2 h led to the pure phase α-CuMoO 4. The different powders obtained were characterized by X ray diffraction analysis and by transmission (TEM) and scanning (SEM) electron microscopies. Ceramics were prepared using conventional sintering and spark plasma sintering (SPS) techniques. A maximal relative density of 94.8% was reached after conventional sintering at 520 1C for 2 h. In the case of SPS, the densification was optimized by varying the temperature, the time and the applied pressure. Higher densities, up to 98.7%, were obtained at very low temperature, i.e., 300 1C, for 5 min only under a pressure of 225 MPa.